1. Field of the Invention
The present invention relates to electronic component packaging, and more particularly, to the packaging of electronic components where thermal transfer is important.
2. Description of Related Art
Resistors have long been packaged individually with each resistive element enclosed in protective covering. The heat generated by such a resistor must be dissipated by the surrounding air requiring a steady air flow through the unit. High power applications may generate more heat than an air cooled system can handle.
Conduction cooled resistors are used in high peak power applications. These resistors, such as the Dale resistors manufactured by the Dale Corporation, generate substantial heat and are surrounded by a conduction cooled jacket that removes the heat generated by the resistors. However, Dale resistors for handling the large peak power demands of certain applications would be abnormally large and would require an inordinate amount of space in the unit.
A third packaging solution has been to mount resistors on a porcelain-on-aluminum base for improved thermal transfer to a heat exchanger. The package is conduction cooled by mounting it on a heat exchange surface, e.g., a water cooled surface. The base is made from a relatively thick piece of aluminum (providing thermal transfer) onto which a thin layer of porcelain is deposited to provide electrical insulation. Resistive elements are held in place, for example, by spun ceramic spacers in an attempt to provide tight thermal contact between the resistive elements and the base.
The above structure is subject to certain limitations, however. The porcelain layer is not highly thermally conductive, limiting the heat transfer from the resistive elements to the aluminum base. The spun ceramic spacers, while providing some pressure to maintain the resistive element and base contact, do not ensure that constant pressure is maintained. Finally, the thin porcelain layer is subject to cracking and fracturing which can lead to failure. Cracking of the porcelain layer exposes the conductive aluminum base to electrical contact with the resistive elements and can lead to failure of the component.
A packaging scheme is needed that provides high thermal transfer and ensures that the components maintain tight thermal contact with the package.